1. Field of the Invention
The present invention concerns an arm device for supporting a rotating element, the end of which is subject to great forces, such as, for example the single support and suspension rear arm of a driving wheel of a motorcycle, in which the rotary support axle of the rotating member is adapted to be maintained rigidly in position in an adjustable manner at the free end of the arm. It also concerns the support arm per se ready to receive the removable bracket piece of the rotary axle as well as the bracket piece of the rotary axle with means that allow it to be rigidly connected, but nevertheless in an adjustable manner, with the support arm.
2. Summary of the Prior Art
Such support arms which constitute first a development of current automobile manufacture, are used on motorcycles in order to support the rear driving wheel of these vehicles. An advantageous adaptation to the motorcycle consists in mounting the rear wheel and the brake disk on the rotary axle on one side of the arm while the sprocket or chain pinion is mounted on the axle on the other side of the arm, thereby allowing rapid wheel change and, where necessary, removal of the brake disk without having to modify the adjustment of the chain. In these wheel mountings on a single arm, the chain tension adjustment is generally performed by means of an eccentric system that carries the high rigidity bearings of the rotary axle. The eccentric system is thus constituted by an accentric bearing support that is caused to rotate there about in a receiving bore in order to adjust the chain tension and which, after adjustment, is blocked by pressing together, i.e. by moving together the lips of a slot opening upon the receiving bore.
These means for adjusting the chain tension have been tested in competition and the maintaining in position of the accentric bearing support by pressing has proved to be reliable and fairly easy to operate. However, these chain tension adjusting means present various drawbacks revealed during use, namely:
precise adjustment of the chain tension has proved to be very difficult to perform in the end stroke zones of the eccentric system., due to the absence of screw positioning means; PA0 adjustment of the chain tension only provides, within admissible limits of required space, a restricted adjustings stroke of about one chain link at the maximum, whereas it would be necessary to dispose of a adjusting stroke exceeding two links; PA0 during the adjustment by rotation of the eccentric bearing support, a variation of the direction of the chain occurs with respect to the support arm which carries the friction chain guides and, sometimes even, has a chain channel passing through it in its zone subjected to the maximal stresses. Such a variation in direction has proved to be prejudicial for the correct guiding of the chain when the chain is at a distance from the central adjusting zone and the need was expressed to return to an adjustment of the chain tension by axial traction; PA0 means for adjusting the chain tension must currently resist chain traction forces that exceed 2000 daN for the small diameter rear wheel chain sprockets, which are necessary in order to limit the chain speeds of high speed motorcycles.
The aim of the present invention is to overcome the defects and drawbacks described herein-above while preserving a chain adjustment that is easy to perform, reliable and simple to manufacture.
With this aim, according to the invention, the free end of the arm comprises plane and generally axial bearing surfaces, adapted to enter into contact with corresponding and generally transversally directed bearing surfaces, provided on a removable bracket piece of the rotary axle, so as to axially guide this bracket piece in order to ensure adjustment of the axial position of the bracket piece and to allow the rigid blocking of this bracket piece on the bearing surfaces of the free end of the arm by a radial pressing wedging upon contact between the said corresponding bearing surfaces which are generally and respectively directed axially and transversally.
According to another embodiment, the axial bearing surfaces provided at the end of the arm are foreseen on the faces of the free end of the arm which are disposed in a polygonal manner, for example square or rectangular, about the median mean line of the arm, whereby the rotation of the bracket piece about this mean median line during the adjustment displacements of the said bracket piece is prevented.
The support arm can comprise, on each face, disposed polygonally and on the side opposite the bearing surfaces, at least one rib destined to ensure the strengthening and the stiffness of the said face. The support arm can also comprise abutment means, adjustable where necessary, adapted to cooperate with corresponding abutment means provided on the bracket piece, in such a manner as to allow the exact adjustment of the axial position of this bracket piece prior to its rigid blocking on the free end of the arm.
According to another embodiment, the bearing surfaces on the free end of the arm are provided on the inner wall of the end of the arm in order to cooperate with corresponding bearing surfaces provided on the external surface of the bracket piece and means for pressing and wedging are provided on the external surface of the end of the arm.
According to another particularly advantageous embodiment of the invention, the bearing surfaces on the free end of the arm are provided on the external faces at the end of the arm in order to cooperate with corresponding bearing surfaces provided on the inner wall of a generally tubular portion of the bracket piece. The other portion of the bracket piece comprises at least one bearing shell in which is provided a bearing bore intended to receive and support the rotary shaft and the tubular portion comprises at least one pressing and wedging means. The corresponding bearing surfaces provided on the inner wall are placed, preferably, along at least two transversel rings, generally annular and protruding from the inside of the said inner wall. Pressing and wedging means are provided opposite each bearing surface ring and is constituted by at least one axial slot provided opposite the transversel ring protruding from the width of this ring, each of the lips of the slot being extended towards the outside by a pressing lug adapted to be crossed through at least partially by a pressing screw. The free end of support arm comprises at least one notch having a generally rounded shape and adapted to receive at least one part of the bearing shell of the bracket piece.
According to another embodiment facilitating the exact adjustment of the position of the bracket piece, at least one axial groove opened towards the outside but closed at the end is provided on at least two substantially diametrically opposed bearing surfaces and is adapted to receive bearing members, for example a spindle or roller plate, interposed between the internal bearing surfaces of the bracket piece and the bottom of the said groove in order to facilitate the axial adjustment movement of the bracket piece with respect to the support arm.
The bracket piece of a rotary axle according to the invention, for example of the axle of a motorcycle rear wheel, intended to be fitted onto or within the free end of a support arm to constitute a previously described support arm device, has a generally tubular form open at one end with bearing surfaces provided on its inner wall, while its other end is closed by a bearing shell intended to receive the rotary axle and its bearing members. The bearing surfaces provided on the bracket piece are disposed according to at least one transversel ring having a generally annular shape and protruding inwardly from the inner wall.
The bracket piece advantageously comprises opposite each bearing surface ring at least one pressing mean constituted by an axial slot each lip of which is extended outwardly by a pressing lug adapted to be crossed through at least partially by a pressing screw. The bracket piece has the general form of a tube with internal or external square or rectangular cross-sections, open at one end and closed at the other by a bearing shell having the general shape of a revolution body, extended outwardly by at least one pivoting bracket lug of a wheel braking member.